WO 99/61307 discloses an apparatus for deploying an object to an underwater target position, the apparatus being provided with a beacon to transmit acoustic rays and a plurality of thrusters to control positioning of the apparatus with respect to the underwater target position.
The prior art apparatus is used for deploying and/or recovering loads up to 1000 tons or more on the seabed at great depths, for instance, up to 3,000 meter or more. During deployment, the apparatus is controlled by controlling equipment on board of a vessel floating on the sea surface. The controlling equipment needs to know the exact location of the apparatus as accurate as possible. To that end, the beacon on board of the apparatus transmits acoustic rays through the sea water to the vessel. An appropriate acoustic receiver receives these acoustic rays and converts them into electrical signals used to calculate the position of the apparatus with respect to the vessel.
However, it is found that with increasing depth of the apparatus below the sea water the accuracy of the location measurement decreases due to bending of the acoustic rays in the sea water.